Structural Prioritization of FatB Thioesterase Candidates Potentially Related to Lauric Acid-Rich Seed Oil in Litsea...

Lauric acid is a characteristic component of Litsea cubeba seed oil, but FatB thioesterase candidates with predicted structural compatibility for C12 acyl-substrate accommodation remain insufficiently defined. In this study, seed oil content and fatty acid composition were examined during L. cubeba seed development. The fatty acid profile shifted from a C18:2-rich pattern at the early stage to a C12:0-dominated composition at later stages, providing the biochemical context for FatB candidate prioritization. Three FatB-like candidates were retrieved from a de novo seed transcriptome assembly and named LcFatB1, LcFatB2, and LcFatB3. Phylogenetic analysis, conserved motif comparison, sequence alignment, and homology modeling showed that LcFatB1 and LcFatB2 retained more complete FatB-like sequence and structural features than LcFatB3. S-dodecanoyl-4'-phosphopantetheine was used as a C12 acyl-4'-phosphopantetheine surrogate for molecular docking. Docking analysis indicated that LcFatB1 and LcFatB2 formed more interpretable C12-bound poses than LcFatB3. Subsequent 150 ns molecular dynamics simulations, free energy landscape analysis, residue-ligand interaction profiling, and catalytic tunnel analysis further distinguished the two main candidates. Compared with LcFatB2, LcFatB1 maintained a lower-displacement C12-bound state, a more compact contact environment involving Tyr116, Ser125, and Asn278, and a main tunnel with higher throughput and shorter length in the representative global-minimum conformation. LcFatB2 also retained the C12 surrogate but stabilized it in a distinct rearranged binding environment. These results support LcFatB1 as the strongest structurally prioritized FatB candidate among the three transcriptome-derived proteins, while LcFatB2 remains a plausible FatB-like candidate with a distinct C12-bound state. This prioritization provides computational structural clues for future biochemical testing but should not be interpreted as direct functional confirmation of FatB activity in vivo.